Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $39.91   8.533%   $43.3155   $43.32   $43.30   $43.30  
  Purchase #2 $190.79   10.868%   $211.5251   $211.53   $211.55   $211.50  
  Purchase #3 $161.31   13.233%   $182.6562   $182.66   $182.65   $182.70  
  Purchase #4 $165.42   11.819%   $184.971   $184.97   $184.95   $185.00  
  Purchase #5 $70.55   12.721%   $79.5247   $79.52   $79.50   $79.50  
  Purchase #6 $106.90   11.758%   $119.4693   $119.47   $119.45   $119.50  
  Purchase #7 $195.41   6.694%   $208.4907   $208.49   $208.50   $208.50  
  7 purchase totals = $930.29       $1,029.9525   $1,029.96   $1,029.90   $1,030.00